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Powdery Mildew: Meg McGrath has just finished up an article reporting her recent research that looked at organic methods for managing powdery mildew of cucurbits. She has kindly allowed me to reprint it here. This is very timely because I am seeing PM moving quickly into fields, especially pumpkins. Fields in early stages of disease development may still be worth treating. Thank you, Meg, for this and all your other work.

Guidelines For Managing Cucurbit Powdery Mildew Organically

Margaret Tuttle McGrath, Department of Plant Pathology, Cornell University, Long Island Horticultural Research and Extension Center; 3059 Sound Avenue, Riverhead, NY 11901; mtm3@cornell.edu; vegetablemdonline.ppath.cornell.edu

Powdery mildew is the most common disease of cucurbit crops occurring every year throughout the US. The characteristic white, powdery fungal growth is readily recognizable on leaves and vines. This growth is mostly spores that are easily dispersed by wind. Symptoms can be difficult to see on watermelon, however, as spores are produced less abundantly than on other cucurbits. Uncontrolled powdery mildew indirectly affects yield because infected leaves usually wither and die. Premature loss of leaves can result in reduced market quality because fruit become sunburnt, have poor color, or have low sugar content due to ripening prematurely or incompletely. Fruit with low sugars have poor flavor and poor storability. Handles on pumpkin fruit may be shriveled or rotten in addition to fruit being paler orange. Size and/or number of fruit can be reduced in summer squash and in other crops when powdery mildew is severe. Severe disease can also lead to imperfections on fruit rind such as speckling and oedema. In addition, powdery mildew infection predisposes plants to other diseases, in particular, gummy stem blight (aka black rot).

Powdery mildew can be managed with resistant varieties and regular foliar applications of disease control products and fungicides*. It is not possible to escape infection because the pathogen produces many wind-dispersed spores, cucurbit crops are grown widely, and conditions often are favorable for this disease. The powdery mildew fungus tolerates a wide range of temperatures below about 100 F and it does not need a period of free moisture on leaves to infect, in contrast with other foliar fungal pathogens. Rain is actually unfavorable. The fungus causing powdery mildew fortunately is sensitive to many types of chemicals that are approved for organic production. These include oil (mineral and botanical types), sulfur, copper, potassium bicarbonate, and biofungicides (Table 1). Efficacy and cost vary widely. Few products are labeled for other diseases. For effective control, applications need to be started very early in disease development and repeated every 7 to 10 days (14 days with resistant varieties). Established powdery mildew cannot be controlled, not even with systemic conventional fungicides. Routine scouting is needed to ensure applications are started very early in powdery mildew development. Plants are susceptible to powdery mildew when in their reproductive phase and at any age when grown under greenhouse conditions. Sometimes symptoms begin to develop on field-grown plants before they begin producing fruit, especially when severely stressed due to delayed transplanting or surrounded by tall weeds; removing these stresses can halt powdery mildew development thereby avoiding the need to start applications early. Inspect plants weekly. When first fruit start to enlarge is an especially important time. The scouting protocol entails weekly examining both leaf surfaces of 5 old, crown leaves in at least 10 locations through out a field. Symptoms develop first on older leaves, often on the underside. It is time to start applications when powdery mildew is found at a very low level on at least 1 of the 50 leaves. Once symptoms are easily seen without hunting, potential to effectively manage powdery mildew with rescue treatments is greatly diminished.

The pathogen develops best on the lower surface (underside) of leaves, thus a successful management program necessitates controlling the pathogen on the lower as well as the upper surface to avoid premature death of leaves.

Unfortunately there are no products with systemic activity approved for organic production and it is difficult to directly deliver fungicide to the lower leaf surface, even with new nozzle types and air assist sprayers. Foliar applications of sulfur have been more effective than most other organic products for powdery mildew on lower surfaces when compared in fungicide efficacy experiments, apparently because when deposited on the upper leaf surface, sulfur can volatilize and be redistributed to the lower surface. Sulfur is also less expensive than other materials. Like copper, sulfur is an element and thus cannot be degraded and removed from the environment as can materials such as oils. Sulfur is a micronutrient for plants. Note that sulfur can be phytotoxic on melons, especially if applied when temperatures are hot.

All products listed in Table 1, except MilStop, have been evaluated in replicated experiments conducted since 1997 in Riverhead, NY, and found to be effective for powdery mildew. All are considered protectants since they do not move into plant tissue. Product efficacy for providing full-season control ranged from poor to at least as good as the popular conventional protectant fungicide chlorothalonil formulated as Bravo. The most effective products were Microthiol Disperss and Eco E-Rase. GC-3 organic fungicide, Organocide, JMS Stylet-oil (organic formulation), and Champion were also highly effective. No experiment included all products thus they cannot be ranked. Tables of these experiment results will be posted on line at http://vegetablemdonline.ppath.cornell.edu/.

In summary, to ensure good yield of high quality fruit of cucurbit crops, manage powdery mildew by selecting varieties with resistance, examining foliage weekly to detect when this disease begins to develop, and applying control products to foliage beginning very early in disease development.

Please Note: Organic growers should ask their certifier about product acceptability for their operation before purchasing. The specific directions on fungicide labels must be adhered to -- they supersede these recommendations if there is a conflict. Any reference to commercial products, trade or brand names is for information only; no endorsement is intended.

* note that in the US products for which the manufacturer claims disease control must be registered as fungicides with EPA unless the ingredients are 'generally recognized as safe' (GRAS) by EPA.

Table 1. Biocompatible products evaluated for managing powdery mildew, active ingredient, whether exempt from tolerance and EPA registration as a fungicide, labeled diseases and insect pests, and company. Note that a few are not yet OMRI listed. A few products are not labeled for use for powdery mildew on cucurbits (target pest must be specified on the label to be used in NY).

1. Bugitol. 0.42% capsaicin and related capsaicinoids, 3.7% allyl isothiocyanate. Kills and repels numerous insects, no diseases on label. Champon Millennium Chemicals. $28.56 at 96 fl oz/A. Not OMRI approved yet. EPA Reg No. 61966-4.
2. Eco E-rase. 97.50% jojoba oil. Controls powdery mildew and white fly. Labeled presently for use on grape and ornamental crops. IJO Products. $16.25 at 0.5% applied at 50 gpa. OMRI listed. Exempt from tolerance. EPA Reg No. 68186-1.
3. GC-3 Organic fungicide. 30% cottonseed oil, 30% corn oil, 23% garlic extract. Controls powdery mildew. JH Biotech, Inc. $23.75 at 1% applied at 50 gpa. OMRI listed. Exempt from EPA registration.
4. Organocide. Active ingredient=5% sesame oil; inerts = 92% fish oil + 3% emulsifiers. Labeled for several diseases and insects. Organic Laboratories, Inc. $47.50 at 2 oz/gal. OMRI listed. Exempt from EPA registration.
5. Sporan. 17.6% rosemary oil; Other ingredient = 82.4% wintergreen oil. Labeled for several fungal diseases. EcoSmart Technologies. $29.25 at 1.5 qt/A. OMRI listed. Exempt from EPA registration.
6. Trilogy. 70% clarified hydrophopic extract of neem oil. Labeled for several diseases and insects. OMRI listed. Certis USA L.L.C. $12.00 at 1% applied at 50 gpa. EPA Reg No. 70051-2.
7. Milsana. 5% ethanolic extract of Reynoutria sachalinensis (giant knotweed). Boosts plants' natural defense mechanisms; certain fungal and bacterial diseases. Label recently expanded from just ornamental greenhouse crops to include use in field on food crops. KHH BioSci, Inc. $8.75 at 2 qt/100 gal applied at 50 gpa. EPA Reg No. 72179-2.
8. Prev-Am. 0.99% sodium tetraborohydrate decahydrate. Labeled for several diseases and insect pests in addition to powdery and downy mildew in cucurbits. ORO Agri, Inc. $11-27.50 at 0.4-1% applied at 50 gpa. EPA Reg No. 72662-3.
9. AgriLife. 5% citric acid. Natural plant immune booster. Broadly labeled for fungi and insects. Biological Solutions, LLC. $30-60 at 0.5-1% applied at 50 gpa. Exempt from EPA registration.
10. JMS Stylet-oil, organic formulation (note that there is another formulation). 97.1% paraffinic oil. JMS Flower Farms, Inc. $7.43 at 5 qt/100 gal applied at 50 gpa. OMRI listed formulation. EPA Reg No. 65564-1.
11. Serenade. Bacillus subtilis. Labeled for several diseases. OMRI listed. AgraQuest. EPA Reg No.69592-11.
12. Sonata. Bacillus pumilus. Labeled for several diseases. OMRI listed. AgraQuest. EPA Reg No. 69592-13.
13. OxiDate. 27% hydrogen dioxide. Labeled for several diseases. OMRI listed. BioSafe Systems. $21.58 at 128 fl oz/100 gal. EPA Reg No. 70299-2.
14. Armicarb. 85% potassium bicarbonate. Labeled for powdery mildew and other diseases. Helena Chemical Company. $12.69-16.92 at 1.5-2 lb/A. EPA Reg No.5905-541.
15. Kaligreen. 82% potassium bicarbonate. Labeled for powdery mildew. $21.41 at 4 lb/A. OMRI listed. AgBio, Inc. EPA Reg No. 70231-1.
16. Milstop. 85% potassium bicarbonate. Labeled for several diseases. BioWorks, Inc. EPA Reg No. 70870-1-68539.
17. Nutrol. potassium dihydrogen phosphate (0-50-32). Labeled for powdery mildew. $11.36-17.04 at 8-12 lb/A. Not OMRI listed. LidoChem, Inc. EPA Reg No. 70644-1.
18. Champion. 77% copper hydroxide. Labeled for several diseases. OMRI listed. NuFarm Americas Inc. $5.70/A at 2 lb/A. EPA Reg No. 55146-1.
19. Microthiol Disperss. 80% sulfur. Labeled for powdery mildew. Will be OMRI listed soon; other sulfur products OMRI listed. Cerexagri. $2.64/A at 4 lb/A. EPA Reg No. 4581-373.

Plectosporium Blight [on Zucchini] (modified from a report by T. Jude Boucher, University of Connecticut, Cooperative Extension System)

Plectosporium blight, caused by the fungus Plectosporium tabacinum (formerly known as Microdochium tabacinum), is a new destructive disease of cucurbits in New England. This disease was found in Tennessee in 1988 and has since spread rapidly throughout the eastern United States. It occurred on a single farm in Massachusetts in 2000 and on at least a dozen farms in Connecticut and Massachusetts in 2003. In the fall of 2004, after two seasons of rainy weather, it was present in every field Jude visited from Long Island Sound to Burlington, Vermont. I am now seeing it this season in Maine on zucchini.

Plectosporium blight is known to cause damage to a wide variety of cucurbit crops in Europe and Asia, but the strain present in the U.S. seems to primarily damage pumpkins, summer squash, zucchini and a few varieties of gourds. In wet years, which favor disease development and spread, crop losses in no-spray and low-spray fields can range from 50 to100%.

Fortunately, this disease is easily recognized but is difficult for organic growers to manage. If you spot it, be prepared to implement good sanitation and develop a effective crop rotation of your cucurbits to clean fields next season.

Description and Management: The clearest symptom to look for on vines and petioles are white lesions that tend to be diamond to lens-shaped; and on fruit and leaves the lesions are usually round and white. [see http://www.umassvegetable.org/soil_crop_pest_mgt/disease_mgt/zucchini_plecto sporium_fruit.html].

Plectosporium blight is favored by cool, rainy weather. The fungus can overwinter on crop residue and can persist in the soil for several years. Plectosporium has not been reported to be seed-borne. Tiny, one or two-celled, sickle-shaped spores are formed in lesions on vines, stems, fruit, leaves and leaf petioles. Spores are dispersed by wind over long distances. Lesions are small (<1/4 inch) and white. The lesions increase in number and coalesce until most of the vines and leaf petioles turn white and the foliage dies. Severely infected pumpkin vines become brittle and will shatter if stepped on . Early in the infection cycle, foliage tends to collapse in a circular pattern before damage becomes more universal throughout the field. These circular patterns can be easily detected when viewing an infected field from a distance. Numerous fruit lesions produce a white russeting on the surface and stems that render the fruit unmarketable. Fruit lesions also allow for entry of soft rot pathogens that hasten the destruction of the crop.

Disease management recommendations include:

∑ a three-year crop rotation
∑ planting in sites with good air circulation to encourage rapid drying of the foliage
∑ switching to trickle irrigation
∑ scouting fields to confirm the presence of Plectosporium, applying fungicides, and plowing under crop residue after harvest
∑ Although there are some fungicides for conventional growers the fungicides available to organic growers are not thought to offer adequate control.

An evaluation of resistance to the disease by different varieties can be found at the web site noted above.

Pepper Maggot Found in New Hampshire (From Alan Eaton, UNH Cooperative Extension)

On July 28th, a Rockingham County pepper grower brought in fruit with unusual deep dimples. I suspected pepper maggot, and set up traps Saturday. By Sunday we had two adults. This is the first time we've found these in New Hampshire. The adults lay eggs in the fruit, and the eggs hatch into maggots that feed especially in the seed head, and it becomes tunneled and rotten. The injury is new to most of us, and you can imagine the reaction of your customers if the fruit they bought has maggots wriggling inside.

If you have fruit with deep dimpled spots here and there, you might have it, too. Hillsborough, Rockingham and possibly southern Strafford Counties are the most likely to be infested. There are controls (see the New England Vegetable Management Guide), but you can't kill the eggs already laid inside the fruit. Here's a link to Jude Boucher's excellent article on pepper maggot and its management, at the UConn Extension IPM page:


TARNISHED PLANT BUGS (modified from an article by Ruth Hazzard in Mass. Veg. Notes) Tarnished plant bug adults and nymphs are being found in several vegetable crops, and in some fields they are causing signifcant damage. We have had calls about damage to the ribs of Romaine lettuce. Most likely it is the second generation of adults that are feeding now. There are several species of tarnished plant bugs in the US, but the most common in central and eastern US is Lygus lineolaris. Adults are about 6 mm long (1/4 inch), brown or tan or greenish with darker markings on their wings and back. Nymphs are bright green and progress through 5 molts (instars) from first hatch to the adult stage. The nymphs can be mistaken for aphids, but move much faster when disturbed. Overwintered adults lay eggs in spring, depositing eggs in stems and leaf ribs in host plants. These adults and nymphs attack strawberry flowers in May. A new generation of adults (which is what we are seeing now) will produce another brood in the late summer, for a total of 2 or possibly 3 generations per year.

Feeding: Adults and nymphs have piercing sucking mouthparts (stylets) which are used to penetrate plant tissues and suck up cellular contents. TPB select succulent, nutritious tissues such as new growth or newly forming fruits (just after blossoming). While feeding, the bugs secrete a toxic substance from their salivary glands, which kills cells surrounding the feeding site. Usually the first signs of damage are small brown spots on young leaves. As the tissue grows, healthy tissue expands while dead tissue does not, which results in holes and distorted, malformed leaves, buds or fruit. Terminal shoots and flowers may be killed.

Damage: Over half of the cultivated crops in the US are listed as hosts. In strawberry, this distorted growth of fruits is known as cat-facing. In lettuce, leaf stems and ribs are injured, causing localized discolored scars and scabs. In celery, feeding on tender stalks produced large, brown colored wilted spots and blacking of joints, know as "blackjoint'. In beans, feeding on flowers causes them to drop, and feeding on seeds in young pods causes pitting and blemishing of pods. In tomatoes, eggplants and peppers, feeding may occur on flowers and stems, causing flower drop, a very common cause for little or late fruit even though the plants are robust. Fruits may also be attacked leading to indentations, bumps, or yellowing of the flesh where the fruit is "stung" by the piercing mouthparts of nymphs or adults. These could be confused with stink bug damage, but they do not have the white pithy areas beneath the skin that is typical of stick bug damage. It is not common to see this damage, but if the damage occurs it may help to determine the cause. In pepper and in basil, feeding in emerging leaves causes distortion and browning of leaves. In apples, adults feed on fruit buds and cause fruit dimpling and scabbing, or dropping off (abscission) of the buds.

Weeds and field crops are also host plants: Tarnished plant bugs attack a large variety of weeds, flowers, forage crops, and orchard crops. Weed hosts include wild carrots and other umbelliferous crops, redroot pigweed (and other amaranths), lambsquarters, mustards, shepardspurse, rocket, goldenrod, and mullein. Alfalfa is a favored host, and harvesting alfalfa often stimulates major lygus migrations. Other legume hosts include vetch, lupine, and fava beans. Where weedy areas or field crops surround vegetable fields, continuous re-infestation of vegetables is possible.

Management: Vegetation management on the whole farm is very important for these highly mobile pests. Focus on removing sources of infestation outside the crop. Disk or rototill weeds along field borders to reduce weed hosts, or keep them mowed all season. Similarly, keep grassy areas on the farm mowed short, to reduce their attractiveness as hosts. However, disturbing non-crop areas by mowing can encourage movement of TPB into your crop, so it should be avoided at critical periods when the crop is vulnerable. There are natural enemies of TPB, including a parasitic wasp, which was released for control of TPB in alfalfa (Peristenus digoneutis). This was released in New Jersey and has spread throughout the Northeast, and can cause up to 50% mortality. However, it currently does not reduce the numbers sufficiently to prevent damage in key crops. Common predators, such as ladybeetles, spined soldier bugs and insidious flower bugs also prey on nymphs. White sticky traps placed above the canopy are used in strawberry and can be used in vegetables to indicate when adults are present. Economic thresholds have been determined for crops where TPB is a key pest, but not in most vegetable crops. It is difficult to sample tarnished plant bugs directly on plants, because they are very mobile and like to hide. In strawberry, nymphs are shaken off the flower clusters onto a flat surface and sprays applied if 4 out of 30 clusters have nymphs. If damage is unacceptably high, use insecticide applications. Labeled products for TPB on lettuce are listed in the 2006-2007 New England Vegetable Management Guide and include Pyganic for organic growers. Avoid applications during bloom periods. Insecticide labels often list "lygus bug" instead of specifcally "tarnished plant bug". --Ruth Hazzard

FLEA BEETLES: PLANT LATE BRASSICAS FAR FROM SPRING CROPS. (from Mass. Veg. Notes) Mid July is often a time of year when adult FB numbers decline, because a large part of the population is underground, in larval and pupal stages. After larvae feed on roots, they pupate in the soil, then emerge again "into the light" as adults-ready to feed on foliage. The time when you will first see these new adults depends on when eggs were first laid on spring Brassica crops, and on soil temperatures since then. Dissections of flea beetles collected from the field in the Connecticut Valley in April and May detected eggs present in early May this year; hence new adults are likely to be emerging now. In fields where Brassica crops are always present, because succession crops are planted close together, it may appear that flea beetles never go away all summer. In fact, they are likely to increase dramatically and feed heavily in early August because of the new summer adults. If you plant fall brassicas close to your spring crops, you make it easy for these beetles to find food. Fall broccoli, cabbage, kale as well as greens such as arugula, bok choi, nappa and salad mix can get heavily damaged or even killed by flea beetle feeding. However if you manage your plantings so that fall brassicas are in a different, separated field than spring crops, you can significantly reduce your problems in fall crops. How far? As far as possible - any distance helps. Barriers such as forest, streams, roads, houses, are helpful. Shorter distances delay the arrival, longer distances delay and reduce the population enough to reduce or eliminate the need for row covers or sprays. At the UMass Research Farm in South Deerfield, flea beetles in brassica crops are still very active and new emergence has been detected. We have succession plantings of brassica crops close together - but in our case, it is on purpose! In conjunction with researchers and farmers in NY and VT, we are testing the use of komastuna as a trap crop around the waxy type of brassicas (broccoli, kale, collard, cabbage, etc). The whole perimeter is planted to one or two rows of komatsuna (a Brassica rapa), which is highly attractive to flea beetle. On an organic farm, the border can be sprayed with Entrust. The organic farm that is testing this (in combination with field rotation to reduce the pressure) has avoided the need for sprays on the main crop. However, greenhouse transplants required a non-heating row cover to keep flea beetles off the seedlings before they reached the field because the greenhouse had a hefty population of flea beetles.

Late Blight Threatens Potatoes [Modified from a report by David Handley in his Sweet Corn IPM Newsletter] Late Blight, caused by Phytophthora infestans, has been found in some commercial potato fields in Maine this summer. This disease can kill all of the plants in a field and ruin the storage life of any surviving tubers. Infections are not limited to large fields. Small plantings can be infected as well. Tomatoes are also susceptible to this disease, and the impact can be just as devastating. Symptoms of late blight start as water-soaked areas on the leaves, usually in the lower portion of the plant. Symptoms tend to first appear in low, poorly-drained areas of a field. The lesions eventually turn black and may have white, fluffy mycelium showing on the underside. [you can sometimes induce the growth of the fluffy mycelium by taking an infected leaf and putting it in a plastic bag over night. This can serve to get an ID]. Lesions on the stem may be brown or black and will eventually lead to the death of the plant.
Infected tubers will have corky lesions that extend into the tissue, and which will eventually lead to soft rot in storage.

Successful management of late blight relies on an integration of the following tactics:

1. Most important is eliminating the source of the pathogen. In Maine Late blight only survives the winter on living tissue such as the potato tuber. Eliminate cull potatoes and volunteers, and plant only healthy seed tubers.
2. Using resistant cultivars when possible and as they become available.
3. Scouting locations where late blight might appear first.
4. Using a forecasting scheme to gain early warning of weather that is favorable to disease and to adjust frequency of scouting and fungicide spraying accordingly. Copper based fungicides that meet NOP standards are the most effect spray available to organic producers. See <http://www.umaine.edu/umext/potatoprogram/> for details on scouting and forecasting info.

Celery- Cercospora blight (Cercospora apii) Symptoms are primarily on the leaves and a bit on the petioles. It starts as chlorotic spots on both lower and upper surface but quickly the spots enlarge and turn brownish and papery in texture. The disease is both seed and soil- borne and it can survive more than two years in seed. It is favored by humid weather. Make sure your seed is clean. Hot water treatment (48 c for 30 minutes) works. Rotate to fields that have been free of the problem for at least two years. Destroy diseased plants.

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